Adsorption-photodegradation of humic acid in water by using ZnO coupled TiO2/bamboo charcoal under visible light irradiation

Enhanced degradation of oxytetracycline in aqueous solution by DBD plasma-coupled vacuum ultraviolet/ultraviolet (VUV/UVC) system

A systematic investigation of coupling dielectric barrier discharge (DBD) plasma and different ultraviolet bands (UVA, UVB, UVC, and VUV) was constructed for antibiotic-contaminant wastewater treatment. Compared with DBD, UV, or other combined DBD/UV systems, the DBD/VUV/UVC system exhibited excellent degradation and mineralization efficiencies for oxytetracycline (OTC), achieving 93.2% removal rate (reaction rate constant 1.05 min^-1) and higher decarbonization efficiency (mineralization rate 0.47 mg C min^-1) within 2.5 min treatment. The radical quenching tests revealed that HO⋅, [Formula: see text] , and ¹O₂ were all involved in the decomposition of OTC in the DBD/VUV/UVC system, among which [Formula: see text] played a dominant role. Possible degradation pathways of OTC in the DBD/VUV/UVC process were proposed using density functional theory and detected intermediates. Four indexes were used to assess the toxicity of OTC and its degraded intermediates. The inorganic anions and HA slightly reduced the degradation efficiency of the DBD/VUV/UVC system. This research provides new ideas to broaden the application of plasma and alleviate the water environment crisis.

A comprehensive appraisal on status and management of remediation of DBPs by TiO2 based-photocatalysts: Insights of technology, performance and energy efficiency

Disinfection has been acknowledged as an inevitable technique in water treatment. However, an inadvertent consequence of generation of carcinogenic and mutagenic disinfection byproducts (DBPs) is associated with the reaction of disinfectants and natural organic matter (NOM) present in water. More than 700 DBPs have been identified in drinking water. The conventional processes carried out in WTPs do not optimally ensure NOM elimination, which evokes the need for the incorporation of other processes. In this context, several physicochemical and advanced oxidation processes (AOP), such as adsorption, membrane techniques, photocatalysis, etc., have been studied for the removal of NOM from water. Photocatalysis using semiconductors has been one of the most proficient technologies, which utilizes light energy for the degradation of recalcitrant organics. The present study aims to provide a comprehensive appraisal on the performance of titanium dioxide (TiO₂) based photocatalysts in the remediation of DBPs concerning the efficacy and energy requirements of the system. Furthermore, the effect of process parameters, such as pH, catalyst dose, light intensity, etc. on the efficacy of the process was also studied. It was observed that conventional P25-TiO₂ powders were efficient in the degradation of dissolved organic carbon (DOC) (up to 90%). However, low photocatalytic activity under visible light activation is one of its significant downsides. Several modifications on the catalyst surface in many studies exhibited advantages, such as high humic acid (HA) degradation under visible light. Furthermore, doped TiO₂ catalysts have shown high total organic carbon (TOC) degradation. The photocatalytic systems have achieved a better decrease in trihalomethane formation potential (THMFP) when compared to haloacetic acid formation potential (HAAFP). The energy requirements of the photocatalytic systems are determined by electrical energy per order (EE/O), which has been observed to be lesser for doped TiO₂ and engineered TiO₂ catalysts when compared with P25-TiO₂ powders. Carbon, iron, silver, etc., based catalysts can be a promising alternative to TiO₂-based photocatalysts for the degradation of NOM, although further research is required in this direction. The present review provides critical highlights on the uses, opportunities, and challenges of TiO₂-based photocatalytic techniques for the management of DBPs and their precursors pertaining to an emerging area of water treatment.

Bifunctional photoelectrochemical process for humic acid degradation and hydrogen production using multi-layered p-type Cu2O photoelectrodes with plasmonic Au@TiO2

Bifunctional photoelectrochemical (PEC) process for simultaneous hydrogen production and mineralisation of humic acid in water using TiO₂-1 wt% Au@TiO₂/Al₂O₃/Cu₂O multi-layered p-type photoelectrodes is demonstrated. The newly designed bifunctional PEC system leads to a high degradation efficiency of dissolved humic compounds, the target pollutant, by up to 87% during 2 h reaction time. Simultaneously, humic acid is also served as a sacrificial electron donor in the proposed system, contributing to a high photocurrent density of the multi-layered p-type Cu₂O photoelectrodes up to -6.32 mA cm^-2 at 0 V vs. Reversible Hydrogen Electrode (RHE) under the AM 1.5 simulated 1-Sun solar illumination. The Z-scheme feature of this bifunctional PEC devices exhibiting a short-circuit photocurrent density of -0.45 mA cm^-2 and solar-to-hydrogen conversion (STH) of 0.5 % in the presence of humic acid sheds light on the new bias-free artificial photosynthesis PEC system.

Study on the preparation of the hierarchical porous CX-TiO2 composites and their selective degradation of PHE solubilized in soil washing eluent

A series of CX-TiO₂(Carbon Xerogel- TiO₂) composites with a hierarchical porous structure were obtained through the sol-gel method followed by drying and carbonization, and have been applied to treating solubilizing wastewater containing a high concentration of phenanthrene (PHE). The characterizations demonstrated that the CX-TiO₂ exhibits a hierarchical porous structure, with particles of carbon and P25 being uniformly in the matrix. Removal efficiency of CX-TiO₂ on PHE in soil washing eluent (SWE) were evaluated under ultraviolet (UV) irradiation or dark condition, and P25 was employed as the reference. The results revealed that CX-TiO₂(0.2) had the best removal effect on PHE, with the efficiency as high as 97.8% under UV illumination within 15 h. It demonstrated that in the process of PHE removal by CX-TiO₂ whether it was under UV illumination or not, the adsorption plays a dominant role in the early stage. The kinetic behavior of PHE adsorption was fitted using the pseudo-first-order and pseudo-second-order, and Langmuir model and Freundlich models were applied to describe the PHE adsorption isotherms. The results indicating that it was a chemical adsorption process, which was influenced by the interaction between PHE and CX-TiO₂, and PHE is adsorbed on the interface of CX-TiO₂(0.2) in a single layer form, instead of agglomerating in the admicelle. A possible mechanism of removal of solubilized PHE in SWE was speculated, in which both hierarchical porous structure and appropriate micropores size of CX-TiO₂ were indispensable to the selective adsorption and degradation of PHE. Recycling performance certificated that the selective removal efficiency of PHE could still reach 82.09% after five recycles. Thus the excellent performance testified that the CX-TiO₂ have great potential in treating SWE containing solubilized PAHs.

Decomplexation of Cu(II)-natural organic matter complex by non-thermal plasma oxidation: Process and mechanisms

Heavy metals and natural organic matters (NOM) form very stable heavy metal-NOM complexes in aqueous, facilitating the migration of heavy metals and enhancing their potential risks. In this study, non-thermal plasma oxidation was attempted to destroy the heavy metal-NOM complexes, with Cu-humate (Cu-HA) as a model. The decomplexation efficiency reached 86.1 % within 50 min of plasma oxidation at 16 kV. The generated reactive species by the non-thermal plasma, including O₂^-, ¹O₂, OH, attacked the carboxyl and hydroxyl functional groups of HA, leading to cleavage of the Cu-O bonds, decomplexation of Cu-HA, and release of free Cu(II). Meanwhile, a variety of small molecular intermediates, including phenols, benzoic acids, esters, amines, ketones, acetic acid, formic acid, and oxalic acid, were generated due to attack by the oxidative species on the aromatic moiety and double bonds in Cu-HA. As a consequence of decomplexation, the residual toxicity of Cu-HA to Scenedesmus obliquus was distinctly reduced. This study provides a potential technique to decomplex heavy metal-NOM complexes, and reduces their toxicity to typical Scenedesmus obliquus.

Photocatalytic Reduction of Cr(VI) in the Presence of Humic Acid Using Immobilized Ce-ZrO2 under Visible Light

Cr(VI) has several industrial applications but it is one of the most dangerous pollutants because of its carcinogenicity and high toxicity. Thus, the removal of Cr(VI) by photocatalytic reduction was investigated. The catalyst applied, Ce–ZrO₂, was immobilized, through a sol–gel process on a silicon carbide (SiC) support, to increase the efficiency and avoid using suspended nanoparticles. The influence of initial pH, humic acid (HA), and catalyst dosage was investigated for Cr(VI) containing solutions. Then, a real galvanizing industry effluent (Cr(VI) = 77 mg L^-1mg.L⁻¹, Zn = 1789 mg L⁻¹) was treated. It was observed that Cr(VI) adsorption and photoreduction are greatly favored at low pH values. HA can decrease Cr(VI) adsorption but also acts as holes scavenger, reducing the electron–hole recombination, favoring then the photoreduction. With the immobilized Ce–ZrO₂, more than 97% of Cr(VI) was removed from the diluted effluent. These results indicate the feasibility to treat Cr(VI) effluents even in the presence of other metals and natural organic matter. The developed material has great chemical and mechanical resistances and avoids the use of nanoparticles, dangerous for the environment and hard to recover. Moreover, solar light can be used to drive the process, which contributes to the development of more sustainable, cleaner, and cost-effective wastewater treatments.

Synthesis and characteristics of a novel FeNi3/SiO2/TiO2 magnetic nanocomposites and its application in adsorption of humic acid from simulated wastewater: study of isotherms and kinetics

The presence of natural organic matter such as humic acid in water creates various problems in water purification. Humic acid can react with chlorine in the disinfection step and lead to the production of trihalomethanes and haloacetic acids that these compounds have carcinogenic and mutagenic properties; therefore, they must be removed before arriving to the disinfection stage. The purpose of this research was adsorption of humic acid from simulated wastewater by synthesized FeNi₃/SiO₂/TiO₂ magnetic nanocomposites. FeNi₃/SiO₂/TiO₂ magnetic nanocomposites were synthesized by sol-gel procedure and its characteristics were determined by TEM, VSM, BET, FESEM, and XRD techniques. Then, the effects of such pH (3-11), FeNi₃/SiO₂/TiO₂ dosage (0.005-0.1 g/L), contact time (0-200 min), and initial concentration (2-15 mg/L) were studied on humic acid adsorption using FeNi₃/SiO₂/TiO₂. The results of adsorption experiments revealed that the highest percentage of humic acid removal (94.4%) was achieved at pH 3, initial concentration of 5 ppm, FeNi₃/SiO₂/TiO₂ dose of 0.1 g/L, and contact time of 90 min. The analyses of experimental isotherm data showed that the humic acid adsorption was described by Langmuir model and also the kinetic studies represented that the process of adsorption of humic acid on FeNi₃/SiO₂/TiO₂ was followed by the pseudo-second kinetic. According to the results, it can be concluded that FeNi₃/SiO₂/TiO₂ magnetic nanocomposites have a high ability to absorb humic acid from simulated wastewater.

Photo-degradation dynamics of five neonicotinoids: Bamboo vinegar as a synergistic agent for improved functional duration

The effects of photo-degradation on the utilization of pesticides in agricultural production has been investigated. Various influencing factors were compared, with results showing that the initial pesticide concentration, light source, water quality and pH possessed different effects on neonicotinoids photo-degradation. The initial concentration and pH were found to be most critical effects. The photo-degradation rate decreased by a factor of 2-4 when the initial concentration increased from 5 mg L-1 to 20 mg L-1, particularly for acetamiprid and imidacloprid. The photo-degradation pathways and products of the five neonicotinoids were also investigated, with similar pathways found for each pesticide, except for acetamiprid. Degradation pathways mainly involved photo-oxidation processes, with products identified using liquid chromatography-quadrupole time-of-flight mass spectrometry (LC-Q-TOF-MS) found to be consistent with literature reported results. Bamboo vinegar exerted a photo-quenching effect on the neonicotinoids, with an improved efficiency at higher vinegar concentrations. The photo-quenching rates of thiamethoxam and dinotefuran were 381.58% and 310.62%, respectively, when a 30-fold dilution of vinegar was employed. The photo-degradation products in bamboo vinegar were identical to those observed in methanol, with acetic acid being the main factor influencing the observed quenching effects.

Visible light-activated degradation of natural organic matter (NOM) using zinc-bismuth oxides-graphitic carbon nitride (ZBO-CN) photocatalyst: Mechanistic insights from EEM-PARAFAC

In this study, the complex degradation behavior of natural organic matter (NOM) was explored using photocatalytic oxidation systems with a novel catalyst based on a hybrid composite of zinc-bismuth oxides and g-C₃N₄ (ZBO-CN). The photooxidation system demonstrated the effective removal of NOM under low-intensity visible light irradiation, presenting removal rates of 53-74% and 65-88% on the basis of dissolved organic carbon (DOC) and the UV absorption coefficient (UV₂₅₄), respectively, at 1.5 g/L of the catalyst. The NOM removal showed an increasing trend with a higher ZBO-CN dose. Comparative experiments with the hole and OH radical scavengers revealed that the direct oxidation occurring on the catalyst's surface might be the governing photocatalytic mechanism. Fluorescence excitation emission matrix-parallel factor analysis (EEM-PARAFAC) revealed the individual removal behavior of the different constituents in bulk NOM. Different tendencies towards preferential adsorption and subsequent oxidative removal were found among dissimilar fluorescent components within a bulk terrestrial NOM, following the order of terrestrial humic-like (C1) > humic-like (C2) > microbial humic-like (C3) components. The result suggests the dominant operation of π-π and/or hydrophobic interactions between the NOM and the catalyst. The discriminative removal behavior was more pronounced in visible light versus UV-activated systems, probably due to the incapability of visible light to excite è - h⁺ pairs of ZnO and the triplet state of NOM. The high photoactivity and structural stability of ZBO-CN under visible light implies its potential for an effective, low-cost and energy-saving treatment technology to selectively remove large sized humic-like substances from water.

Control of Membrane Fouling in Organics Filtration Using Ce-Doped Zirconia and Visible Light

Membrane fouling has been a major issue in the development of more efficient water treatment processes. Specifically in surface waters filtration, organic matter, such as humic-like substances, can cause irreversible fouling. Therefore, this study evaluates the activity of a photocatalytic layer composed of Ce-doped zirconia nanoparticles in improving the fouling resistance during filtration of an aqueous solution of humic acid (HA). These nanoparticles were prepared by hydrothermal and sol-gel processes and then characterized. Before the filtration experiments, the photodegradation of HA catalyzed by Ce-doped zirconia nanoparticles in dispersion was studied. It was observed that the sol-gel prepared Ce-ZrO₂ exhibited higher HA removal in practically neutral pH, achieving 93% efficiency in 180 min of adsorption in the dark followed by 180 min under visible-light irradiation using light-emitting diodes (LEDs). Changes in spectral properties and in total organic carbon confirmed HA degradation and contributed to the proposal of a mechanism for HA photodegradation. Finally, in HA filtration tests, Ce-ZrO₂ photocatalytic membranes were able to recover the flux in a fouled membrane using visible-light by degrading HA. The present findings point to the further development of anti-fouling membranes, in which solar light can be used to degrade fouling compounds and possibly contaminants of emerging concern, which will have important environmental implications.

Photodegradation of pharmaceuticals and personal care products in water treatment using carbonaceous-TiO2 composites: A critical review of recent literature

The high concentrations of pharmaceuticals and personal care products (PPCP) that found in water in many locations are of concern. Among the available water treatment methods, heterogeneous photocatalysis using TiO₂ is an emerging and viable technology to overcome the occurrence of PPCP in natural and waste water. The combination of carbonaceous materials (e.g., activated carbon, carbon nanotubes and graphene nanosheets) with TiO₂, a recent development, gives significantly improved performance. In this article, we present a critical review of the development and fabrication of carbonaceous-TiO₂ and its application to PPCP removal including its influence on water chemistry, and the relevant operational parameters. Finally, we present an analysis of current priorities in the ongoing research and development of carbonaceous-TiO₂ for the photodegradation of PPCP.

Advanced oxidation processes for the removal of natural organic matter from drinking water sources: A comprehensive review

Natural organic matter (NOM), a key component in aquatic environments, is a complex matrix of organic substances characterized by its fluctuating amounts in water and variable molecular and chemical properties, leading to various interaction schemes with the biogeosphere and hydrologic cycle. These factors, along with the increasing amounts of NOM in surface and ground waters, make the effort of removing naturally-occurring organics from drinking water supplies, and also from municipal wastewater effluents, a challenging task requiring the development of highly efficient and versatile water treatment technologies. Advanced oxidation processes (AOPs) received an increasing amount of attention from researchers around the world, especially during the last decade. The related processes were frequently reported to be among the most suitable water treatment technologies to remove NOM from drinking water supplies and mitigate the formation of disinfection by products (DBPs). Thus, the present work overviews recent research and development studies conducted on the application of AOPs to degrade NOM including UV and/or ozone-based applications, different Fenton processes and various heterogeneous catalytic and photocatalytic oxidative processes. Other non-conventional AOPs such as ultrasonication, ionizing radiation and plasma technologies were also reported. Furthermore, since AOPs are unlikely to achieve complete oxidation of NOM, integration schemes with other water treatment technologies were presented including membrane filtration, adsorption and others processes.

Photocatalytic degradation of P-Cresol using TiO2/ZnO hybrid surface capped with polyaniline

This study evaluated the photocatalytic activity of polyaniline (PANI)-capped titanium dioxide and zinc oxide (TiO₂/ZnO) hybrid, for the degradation of P-Cresol. The hybrid was synthesized by precipitating ZnO on the surface of commercial TiO₂. An "in situ" chemical oxidative polymerization method was used to prepare the PANI capped hybrid (TiO₂/ZnO/PANI). The photocatalysts were characterized by powder X-ray diffraction (XRD), a Brunauer Emmett Teller (BET) analyzer, Fourier-transform infrared (FTIR) and photoluminescence spectroscopies, high resolution-transmission electron microscopy (HR-TEM) and thermogravimetric analysis (TGA). During photodegradation under ultraviolet (UV) irradiation, ZnO, TiO₂, TiO₂/ZnO hybrid and TiO₂/ZnO/PANI composite had P-Cresol removal of 43%, 50%, 61% and 99%, respectively. The higher activity of the TiO₂/ZnO hybrid as compared to TiO₂ and ZnO was attributed to a reduced electron-hole pair recombination. The recombination was further significantly reduced upon introduction of PANI; hence, the highest activity observed with TiO₂/ZnO/PANI. The initial reaction rate constant for TiO₂/ZnO/PANI (0.9679 min^-1) was more than twice compared to that for TiO₂/ZnO hybrid (0.1259 min^-1). A synergistic effect between PANI and TiO₂/ZnO resulted in a highly efficient charge separation caused by the transfer of photogenerated holes from the hybrid to highest occupied molecular orbitals (HOMO) of PANI. The best TiO₂/ZnO/PANI (PANI to TiO₂/ZnO) ratio observed was 0.5:2 for the photodegradation of P-Cresol. Total organic carbon (TOC) analysis indicated a 97.4% mineralization of P-Cresol with PANI/TiO₂/ZnO.

Photodecolorisation of melanoidins in vinasse with illuminated TiO2-ZnO/activated carbon composite

A hybrid photo-catalyst, TiO₂-ZnO, was synthesized by immobilizing ZnO on commercial TiO₂ (aeroxide P25). Activated carbon (AC) was subsequently used to support the hybrid, thus forming a TiO₂-ZnO/AC composite catalyst. Fourier transform infrared (FTIR) analysis and scanning electron microscopy integrated with energy-dispersive X-ray spectroscopy (SEM-EDX) investigations revealed successful catalyst synthesis. Optical properties of the hybrid determined from photoluminescence (PL) and Ultraviolet-visible (UV-vis) spectroscopy confirmed a restrained recombination of electron-hole pairs and reduced energy band gap due to a successful heterojunction formation. The prepared catalysts were used to photodecolorise vinasse in a 12-W UVC batch photoreactor. TiO₂-ZnO had improved photocatalytic activity compared with TiO₂ and ZnO separately. On supporting the hybrid onto AC, both adsorption and photocatalytic activities were further enhanced with improved overall color removal of 86% from 68%. Photodecolorisation followed the pseudo-first-order reaction model with the rate constant ([Formula: see text]) observed decreasing from 0.0701 to 0.0436 min^-1 on increasing the initial concentration from 5,000 to 14,000 ppm. The UV process was found to be 33-fold less energy intensive for color reduction as compared to total organic carbon (TOC) reduction. Formation of nitrates during the photodecolorisation process was attributed to the mineralization of nitrogen heteroatoms in the color-causing melanoidin compounds.

Solvothermal syntheses of Bi and Zn co-doped TiO2 with enhanced electron-hole separation and efficient photodegradation of gaseous toluene under visible-light

This study investigated the effects of Bi doped and Bi-Zn co-doped TiO₂ on photodegradation of gaseous toluene. The doped TiO₂ with various concentration of metal was prepared using the solvothermal route and characterized by SEM, XRD, Raman, BET, DRS, XPS, PL and EPR. Their photocatalytic activities under visible-light irradiation were drastically influenced by the dopant content. The results showed that moderate metal doping levels were obviously beneficial for the toluene degradation, while high doping levels suppressed the photocatalytic activity. The photocatalytic degradation of toluene over TiBi_1.9%O₂ and TiBi_1.9%Zn_1%O₂ can reach to 51% and 93%, respectively, which are much higher than 25% of TiO₂. Bi doping into TiO₂ lattice generates new intermediate energy level of Bi below the CB edge of TiO₂. The electron excitation from the VB to Bi orbitals results in the decreased band gap, extended absorption of visible-light and thus enhances its photocatalytic efficiency. Zn doping not only further enhances the absorption in this visible-light region, but also Zn dopant exists as the form of ZnO crystallites located on the interfaces of TiO₂ agglomerates and acts as a mediator of interfacial charge transfer to suppress the electron-hole recombination. These synergistic effects are responsible for the enhanced photocatalytic performance.

Efficient visible light-driven in situ photocatalytic destruction of harmful alga by worm-like N,P co-doped TiO2/expanded graphite carbon layer (NPT-EGC) floating composites

Preparation of N,P co-doped TiO₂/expanded graphite carbon layer (NPT-EGC) composites for floating algaecides.

Evaluation of the potentials of humic acid removal in water by gas phase surface discharge plasma

Degradation of humic acid (HA), a predominant type of natural organic matter in ground water and surface waters, was conducted using a gas phase surface discharge plasma system. HA standard and two surface waters (Wetland, and Weihe River) were selected as the targets. The experimental results showed that about 90.9% of standard HA was smoothly removed within 40 min's discharge plasma treatment at discharge voltage 23.0 kV, and the removal process fitted the first-order kinetic model. Roles of some active species in HA removal were studied by evaluating the effects of solution pH and OH radical scavenger; and the results presented that O3 and OH radical played significant roles in HA removal. Scanning electron microscope (SEM) and FTIR analysis showed that HA surface topography and molecular structure were changed during discharge plasma process. The mineralization of HA was analyzed by UV-Vis spectrum, dissolved organic carbon (DOC), specific UV absorbance (SUVA), UV absorption ratios, and excitation-emission matrix (EEM) fluorescence. The formation of disinfection by-products during HA sample chlorination was also identified, and CHCl3 was detected as the main disinfection by-product, but discharge plasma treatment could suppress its formation to a certain extent. In addition, approximately 82.3% and 67.9% of UV254 were removed for the Weihe River water and the Wetland water after 40 min of discharge plasma treatment.

Enhanced visible light photocatalytic activity of a floating photocatalyst based on B–N-codoped TiO2 grafted on expanded perlite

Floatable photocatalyst for in situ environmental remediation with enhanced visible light driven photocatalytic activity.

Bioframe synthesis of NF–TiO2/straw charcoal composites for enhanced adsorption-visible light photocatalytic degradation of RhB

N–F codoped TiO₂/straw charcoal composites (NF–TiO₂/SC) were synthesized using a simple, bioframe-assisted sol–gel method and confirmed by XRD, SEM, EDX, TEM, N₂ adsorption–desorption, Raman, FT-IR, XPS, and UV-vis DRS measurements.

Synthesis, characterization and visible light photocatalytic activity of Cr3+, Ce3+and N co-doped TiO2for the degradation of humic acid

The synthesis, characterization and photocatalytic activity of Cr³⁺and Ce³⁺co-doped TiON (N-doped TiO₂) for the degradation of humic acid with exposure to visible light is reported.

Effect of porous zinc–biochar nanocomposites on Cr(vi) adsorption from aqueous solution

A new synthesis method was developed to produce zinc–biochar nanocomposites from sugarcane bagasse.

Humic acid degradation by the synthesized flower-like Ag/ZnO nanostructure as an efficient photocatalyst

Nano-sized flower-like Ag/ZnO was synthesized by a simple method using zinc acetate and silver acetate under hydrothermal condition. Powder X-ray diffraction (PXRD) and transmission electron microscopy (TEM) were used to characterize the structure and morphology of the synthesized powder. Nano flower-like Ag/ZnO was used as a photocatalyst for degradation of humic acid in aqueous solution. The disappearance of HA was analyzed by measuring the absorbance of sample at special wavelength (254 nm). The effects of various parameters such as amount of photocatalyst, pH, initial humic acid concentration and irradiation time on degradation rate were systematically investigated. Photodegradation efficiency was small when the photolysis was carried out in the absence of Ag/ZnO and it was also negligible in the absence of light. Approximately 70% of humic acid (50 mg/L) has been eliminated after 40 minutes in the presences of catalyst (catalyst dose o.6 g/L and pH =7) and UVA irradiation. While, 100% of humic acid has been eliminated with solar irradiation.